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what 30mm to 50mm class eyepiece are you using with your SCT/ACF/Edge ?

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#26 YAOG

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Posted 19 September 2019 - 04:05 PM

I am waiting for the big XWs to return as well.

I understand you are going to be happy soon.


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#27 YAOG

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Posted 19 September 2019 - 04:12 PM

I have a question, do many people use the Celestron 0.63x reducer/corrector visually? 

 

I know that it effectively reducers the focal length of the scope but what does it "correct?"

 

If so what have you noticed about the outer 1/3 of the field with widefield eyepieces vs narrower AFOVs like Orthos and Plossls? 

 

Where does vignetting start in terms of AFOV and eyepiece focal length on which scopes 8" 9.25" 10" 11" 12" 14"? 


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#28 jhbanister

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Posted 19 September 2019 - 06:42 PM

41mm and 35mm Pans

Ditto, plus a 28mm ES 68.


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#29 25585

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Posted 20 September 2019 - 12:11 AM

My longest FL 1.25" eps are TV 40mm Plossl, Vixen LV 40mm, Celestron Ultima 35mm and LER 32mm, and a Takahashi 28mm Erfle.  


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#30 Jon Isaacs

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Posted 20 September 2019 - 06:05 AM

I have a question, do many people use the Celestron 0.63x reducer/corrector visually? 

 

I know that it effectively reducers the focal length of the scope but what does it "correct?"

 

If so what have you noticed about the outer 1/3 of the field with widefield eyepieces vs narrower AFOVs like Orthos and Plossls? 

 

Where does vignetting start in terms of AFOV and eyepiece focal length on which scopes 8" 9.25" 10" 11" 12" 14"? 

This is how I understand it:

 

The Celestron F/6.3 reducer/corrector was designed for the C-8 to use with the 35mm film cameras of the day.  The 35m frame is actually 36mm x 24mm.  The rear port of a C-8 is 38mm and 38mm x 0.63= 24mm. This means a C-8 with a F/6.3 would provide a fully illuminated circle that matches the short dimension of the film frame.

 

As to what it corrects for, I believe it supposed to correct for field curvature and possibly coma.  I think it helps but is not well corrected like the Edge.

 

I have only used the F/6.3 in a C-5 and a C-8 and that has been some years.  I do know that I was able to achieve a 1.85 degree TFoV with a 32mm Plossl with the C-5.  The edge of the field was heavily vignetted.  

 

A calculation based on the 0.63 reduction and the 1250mm focal length of the C-5 says that particular Plossl (27.5mm field stop) should provide a 2.00 degree TFoV but both those numbers are questionable because they both depend on spacing.  

 

That's about what I can offer.

 

Jon


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#31 sanbai

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Posted 20 September 2019 - 07:04 AM

I have a question, do many people use the Celestron 0.63x reducer/corrector visually?

I know that it effectively reducers the focal length of the scope but what does it "correct?"

If so what have you noticed about the outer 1/3 of the field with widefield eyepieces vs narrower AFOVs like Orthos and Plossls?

Where does vignetting start in terms of AFOV and eyepiece focal length on which scopes 8" 9.25" 10" 11" 12" 14"?


An advantage for some people may be getting the widest field possible using 1.25" eyepieces and diagonal. It saves you the cost of more expensive 2" eyepieces and diagonal, you can use the reducer for AP, and you get the correction too (cheaper than getting an edgeHD).

So, a 2" 55mm Plössl can be replaced by a 1.25" 32 mm with reducer. The actual number would be 35mm, but the EP field stop would not allow 50 ° AFOV. Actually the shorter FL due to shorter spacing needed with a 1.25 diagonal may compensate that in terms of TFOV.

You cannot get wider field anyway, the internal baffles of the telescope would not allow it, except with heavy vignetting, as said above.

I went the 2" way. I actually did not know then what I said above, but don't regret anyway.

Edited by Santiago Barroso, 20 September 2019 - 07:06 AM.


#32 Daniel Mounsey

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Posted 20 September 2019 - 07:07 AM

I am waiting for the big XWs to return as well.

 

The 30XW and 40XW are expected back out by December.


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#33 Daniel Mounsey

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Posted 20 September 2019 - 07:29 AM

Several months ago I did a side by side comparison using an 8" XLT SCT with 6.3 reducer and an 8" Edge HD with a .7x Edge reducer. I used two types of diagonals for my tests. One was the dedicated Celestron 2" "SCT thread on" diagonal. Using a 35 Panoptic, there was absolutely no visible vignetting whatsoever in either scope. I asked a couple of the employees to have a look while switching between the two scopes and it was practically impossible for them to tell any difference.

 

Next, I attached a standard 2" compression ring SCT adapter, then inserted a 2" Televue Everbrite diagonal into each scope while still using the dedicated reducers in each one. While using the 35 Panoptic, there was still absolutely no visible vignetting whatsoever in either scope. 35 Panoptic field stop diameter is 38.7mm. More to come.



#34 Piero DP

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Posted 20 September 2019 - 08:11 AM

The 30XW and 40XW are expected back out by December.


Do you have a link for this?
Thanks.

#35 Daniel Mounsey

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Posted 20 September 2019 - 08:23 AM

Not that I’m aware of. This was announced to us by our Pentax rep.

#36 Hesiod

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Posted 20 September 2019 - 10:33 AM

Several months ago I did a side by side comparison using an 8" XLT SCT with 6.3 reducer and an 8" Edge HD with a .7x Edge reducer. I used two types of diagonals for my tests. One was the dedicated Celestron 2" "SCT thread on" diagonal. Using a 35 Panoptic, there was absolutely no visible vignetting whatsoever in either scope. I asked a couple of the employees to have a look while switching between the two scopes and it was practically impossible for them to tell any difference.

 

Next, I attached a standard 2" compression ring SCT adapter, then inserted a 2" Televue Everbrite diagonal into each scope while still using the dedicated reducers in each one. While using the 35 Panoptic, there was still absolutely no visible vignetting whatsoever in either scope. 35 Panoptic field stop diameter is 38.7mm. More to come.

Did you measured the field of view in the C8+reducer+SC-type stardiagonal?

Also, how about coma? I tried my c8 with a 25mm/80° and a 40mm/68° without corrector, and in both cases did not like the result due to coma


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#37 YAOG

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Posted 20 September 2019 - 10:47 AM

It seems to me that the limitation on FOV is the size of the entry to the baffle tube in an commercial SCT. AFAIK the baffle tube entrance acts as a natural field stop and nothing falling outside the ID of the tube will be seen.


Edited by YAOG, 20 September 2019 - 03:22 PM.


#38 Jon Isaacs

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Posted 20 September 2019 - 10:54 AM

It seems to me that the limitation on FOV is the size of the entry to the baffle tube in an commercial SCT. AFAIK the baffle tube entrance acts as a natural filed stop and nothing falling outside the ID of the tube will be seen.

 

It seems that way but it does really workout that way.  The reason is that the aperture stop is not at the focal plane, it's out of focus. 

 

Just how far you can go before the vignetting becomes apparent is hard to say but the eye is very forgiving of vignetting, a camera will see it, the eye won't.  Most telescopes do not fully illuminate the entire focal plane..

 

Jon



#39 Tom Masterson

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Posted 20 September 2019 - 11:07 AM

Meade series 5000 30mm toe crusher, and "vintage" 2" 32mm University Optics Widescan.


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#40 YAOG

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Posted 20 September 2019 - 11:28 AM

It seems that way but it does really workout that way.  The reason is that the aperture stop is not at the focal plane, it's out of focus. 

 

Just how far you can go before the vignetting becomes apparent is hard to say but the eye is very forgiving of vignetting, a camera will see it, the eye won't.  Most telescopes do not fully illuminate the entire focal plane..

 

Jon

Well of course that's true but is seems like there should be few useful Ray's outside the baffle ID. Everything else, Ray's outside the proper light cone seems like it would not be helpful to forming an image and would be more like scattered random rays reducing contrast. 

 

We could see what removing the baffle tube does and see if the FOV gets any wider and if the size of the image circle illumination gets bigger and if it reduces contrast. 

 

Also from what I have read in the SCT design books all SCTs have a designed distance from the secondary where everything is supposed to meet the designed performance for focal length, abberrations, FOV etc. When we move the mirror to focus these newer designed long wide AFOV eyepieces don't we mess up other elements of the image? 



#41 Daniel Mounsey

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Posted 20 September 2019 - 12:12 PM

It seems that way but it does really workout that way.  The reason is that the aperture stop is not at the focal plane, it's out of focus. 

 

Just how far you can go before the vignetting becomes apparent is hard to say but the eye is very forgiving of vignetting, a camera will see it, the eye won't.  Most telescopes do not fully illuminate the entire focal plane..

 

Jon

Chip, what Jon is saying here is correct. 



#42 Daniel Mounsey

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Posted 20 September 2019 - 12:22 PM

Did you measured the field of view in the C8+reducer+SC-type stardiagonal?

Also, how about coma? I tried my c8 with a 25mm/80° and a 40mm/68° without corrector, and in both cases did not like the result due to coma

 

Everything appeared to perform to spec as far as FOV. During the day, it's harder to read coma but even for the guys while looking around the very outer field of view in the 35 Panoptic in each scope, they were having too difficult a time making out any noticeable difference between the SCT and Edge. The coma in an SCT is about equivalent to an F6/7 Newtonian. That's not too bad.  


Edited by Daniel Mounsey, 20 September 2019 - 12:23 PM.


#43 Hesiod

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Posted 20 September 2019 - 12:59 PM

Not so good eitherlol.gif ...so the focal ended up in the 1200s? That's would be interesting. Did you had the impression that the Celestron SCT diagonal is "shorter" than other, similar products?



#44 Jon Isaacs

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Posted 20 September 2019 - 01:08 PM

Everything appeared to perform to spec as far as FOV. During the day, it's harder to read coma but even for the guys while looking around the very outer field of view in the 35 Panoptic in each scope, they were having too difficult a time making out any noticeable difference between the SCT and Edge. The coma in an SCT is about equivalent to an F6/7 Newtonian. That's not too bad.  

 

Daniel:

 

If you're conducting the test during the day, mild vignetting might be masked to some extent by the observers reduced pupil. 

 

My night time experiences with a C-5 and 2 inch eyepieces as well as with the F/6.3 reducer were quite surprising, I certainly expected to see serious vignetting but it just wasn't visible except in the most extreme cases.

 

The eye is not a camera, a camera shows it immediately but gradual off-axis reduction in brightness is difficult to see and exists in nearly every scope, including refractors, that are not designed with astrophotography in mind. This is why there are so many refractors with 2.7 inch and larger Focusers, imaging.

 

Any explanation I can offer is really only hand waving to try to explain what I see at the eyepiece. It is something you really just have to experience.. 

 

Jon


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#45 Daniel Mounsey

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Posted 20 September 2019 - 01:47 PM

Jon, you raised good points and there are several reasons why we need to do some tests during the night. We got a little something planned for next weekend with the guys.

#46 Daniel Mounsey

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Posted 20 September 2019 - 02:05 PM

Not so good eitherlol.gif ...so the focal ended up in the 1200s? That's would be interesting. Did you had the impression that the Celestron SCT diagonal is "shorter" than other, similar products?

 

As my old observing buddy Vernon use to say.... I’m not married to the edge of field. The reason for each diagonal was to remove any doubt about them affecting the image.


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#47 makeitso

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Posted 20 September 2019 - 02:10 PM

I can tell you that a 35 panoptic (thanks Jon Isaacs for loaning it to me) in my C6 with the .63 reducer is vignette city.

 

Sort of like look out the entrance of a cave.

 

Jack



#48 Jon Isaacs

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Posted 20 September 2019 - 02:14 PM

I can tell you that a 35 panoptic (thanks Jon Isaacs for loaning it to me) in my C6 with the .63 reducer is vignette city.

 

Sort of like look out the entrance of a cave.

 

Jack

 

Jack:

 

No surprise there, the C-6 has the same 1 inch rear port as the C-5 so with the reducer, the effective diameter of the port is about 16mm.. 

 

Did you try the 35mm Pan on the C-6 without the reducer?

 

I should add that Glenn LeDrew has experienced this and has a good explanation.. 

 

Jon


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#49 eklf

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Posted 20 September 2019 - 03:24 PM

I have a question, do many people use the Celestron 0.63x reducer/corrector visually? 

 

I know that it effectively reducers the focal length of the scope but what does it "correct?"

 

If so what have you noticed about the outer 1/3 of the field with widefield eyepieces vs narrower AFOVs like Orthos and Plossls? 

 

Where does vignetting start in terms of AFOV and eyepiece focal length on which scopes 8" 9.25" 10" 11" 12" 14"? 

In a wide field, in my expereince, the reducer/corrector in a C8  improves the quality the most in the middle third - the outer third improvement is not dramatic... but its there.

 

Vignetting - 22t4 showed mild but detectable vignetting, 20mm APM 100 deg showed somewhat more, but still acceptable to me.

 

My most used in my C8 (with the reducer) is ES 28mm 68deg, and 22mm LVW.

 

With a screw on 2 inch diagonal and the reducer, the focal length is about 1360ish mm (exact value depended on each eyepeice)


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#50 YAOG

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Posted 20 September 2019 - 03:31 PM

It seems that way but it does really workout that way.  The reason is that the aperture stop is not at the focal plane, it's out of focus. 

 

Just how far you can go before the vignetting becomes apparent is hard to say but the eye is very forgiving of vignetting, a camera will see it, the eye won't.  Most telescopes do not fully illuminate the entire focal plane..

 

Jon

 

 

Chip, what Jon is saying here is correct. 

 

Well I'm sure what Jon is saying correct is to the extent that the baffle tube will offer a soft field stop without a hard edge because it is not close enough to the plane of focus. But where would the any other wider rays come from outside the light cone that passed the end of baffle tube? I think this is demonstrable using a laser and seeing where the baffle tube cutoff point is.  




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